ANTIGEN = any molecule to which a specific immune response can
be generated:

specific means that lymphocytes are activated;

antigens are usually foreign but not always.

proteins and carbohydrates are good antigens.

antigens can be soluble or insoluble.

cells and particles are really aggregates of antigens.

(but we often refer to bacteria, viruses, etc. as antigen - this is
imprecise but OK as long as you remember that there are many antigens associated
with these).

some molecules (small) are not immunogenic, but if attached to something
bigger then they will become antigenic. these things are called HAPTENS.

microbes / cells are a composite or aggregate of antigens. each antigen
on a bacterial cell will provoke a unique specificity of antibody. See
page 428 Tortora.

moreover, somtimes antigens on different (unrelated) cells are similar
enough so that an antibody made to one will react with another. this is
a cross-reaction.

an antigen is actually composed of multiple antigenic determinants or
EPITOPES. Antibodies are made to the epitopes. A hapten is like
a free epitope. Look at the pictures on pgs 428 - 430; figs.17.4 , 17.5
and 17.6.

ANTIBODIES

There are FIVE CLASSES OF ANTIBODIES, the molecules of each class
have the same basic structure. See fig 17.6 (pg430) and table 17.1 (page
431).

g.) urea will be broken down to ammonia by the urease only if human-anti-virus
antibody is present. (Why?) Ammonia will cause the pH to become basic and
the pH indicator will change color. The color change is a convenient indicator
that the human antibody is there.

2.) FLUORESCENT ANTIBODY TECHNIQUES

FLUORESCENT MICROSCOPY -- ( See Tortora pg.458, fig.18.13)

a.) Reagent antibody labeled with fluorescent dyes (FITC and TRITC).

b.) React the antibody with a specimen believed to contain the antigen.

c.) Observe under a fluorescent microscope (ultraviolet light excites
fluorescent dye to emit visible light), if the antigen is there it will
glow.